This invention relates, in general, to rotating turbomachines and to turning gears for rotating a turbine rotor when motive fluid is insufficient to cause the rotation of the turbine rotor. In particular, this invention further relates to a hydraulic system and associated turning gear which is reduced in size for shipboard applications and which utilizes low pressure hydraulic fluid in combination with pressure boost means to provide sufficient turning power despite the reduced size of the equipment.
Rotating machinery such as turbines, including steam turbines or gas turbines, require means associated with the rotating machinery to turn the turbine rotor whenever the motive fluid, steam or gas, is insufficient to cause the rotor to turn but while the rotor is at an elevated temperature such as during periods of warm-up, cool-down or if the supply of motive fluid is shutdown for some reason. The reason for utilizing a turning gear on a heated rotor is that if the rotor is not turned under these conditions it will develop or bow or sag as thermal conditions change which could result in the turbomachine being rendered inoperative.
One way of rotating a turning gear in through the use of an electric motor which is coupled to the rotor. However, in this arrangement, the motor must be located adjacent the turbine rotor and as the power requirements for rotating the turbomachine rotor increase the size of the motor must also increase such that it has been found difficult to meet the envelope requirements of the turbine environment. Also, with the increase in size of the motor there is also an increase in weight which is an undesirable characteristic in modern ship power plants. Another compromising feature of electric motors used as turning gear drivers occurs under complete loss of power conditions where the turbomachine rotor could be severely endangered if rotation is not effected.
Another means for rotating a turbomachinery rotor is through the use of a hydraulic turning gear wherein hydraulic fluid is used to drive a hydraulic cylinder which, in turn, drives a ratchet and pawl mechanism for turning the turnbomachine rotor. This type of apparatus is generally smaller, lighter weight, able to function by means of a handpump or manual valve control for emergency operation and less expensive. However, as power requirements for rotating the turning gear have increased, the size of the hydraulic equipment has also been caused to increase. For example, one main piece of equipment in the hydraulic turning gear system which must be placed in the vicinity of the turning gear is the hydraulic cylinder. Using low pressure oil (100 psi) as the driving fluid would result in a ten inch diameter hydraulic cylinder in a very crowded space near the turbine equipment. The low pressure hydraulic fluid is preferred since it is also used for lubrication fluid therefore allowing the use of a single fluid supply. In one aspect of this invention it has been found that the size of the hydraulic cylinder may be reduced to a two inch diameter hydraulic cylinder if the pressure of the hydraulic fluid to the driving side of the hydraulic cylinder is raised after it has been withdrawn from a common reservoir. The reservoir is remotely located with respect to the hydraulic cylinder and therefore does not add to the size requirements of the turbine equipment envelope and by reducing the size of the hydraulic cylinder makes the turning gear apparatus more fittable into the turbine environment.
A booster cylinder provides a desirable means for raising the pressure of the hydraulic fluid prior to the introduction of the fluid into the hydraulic cylinder of reduced size.
The hydraulic cylinder motivates a ratchet and pawl mechanism for turning the turning gear wheel. Realizing that this means that the pawl which engages the ratchet wheel must pivot to engage and disengage from the ratchet wheel several times in each shaft revolution, the disadvantage of a spring return for the pawl is the noise it may create as it hits after each tooth. According to another feature of the present invention, the pawl of the present invention utilizes frictional force to withhold the pawl from the ratchet wheel and then uses a positively driven reset to realign the pawl with the ratchet wheel thus obviating the use of a noise producing spring.
It is therefore an object of the present invention to provide a hydraulic turning gear which provides an elevated pressure fluid to a hydraulic cylinder of reduced size for driving the turning gear.
It is another object of the present invention to provide a means for raising the hydraulic fluid pressure at a location inline and removed from the fluid reservoir.
It is another object of the present invention to provide a pawl mechanism which will produce a quiet return of the pawl to the ratchet wheel.
The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood with reference to the following description and drawings.